1. Field of the Invention
The present invention relates to a spunbonded fabric of continuous thermoplastic filaments, and to a process for its production.
Biodegradable nonwoven fabrics made up of staple fibers are known: The use of viscose fibers is described by I. Marini, in Allg. Vliesstoff-Report [General Report on Nonwovens] 1986, Vol. 14, No. 4, page 214 f.
These biodegradable fibers are natural fibers and natural fiber derivatives. Fields of application include disposable utility goods, such as diapers for children and incontinents, mattress covers, surgical scrub suits and drapery, and bandage holders.
The term biodegradable should be understood herein to mean that complete destruction of the fibrous or nonwoven material is effected by means of microorganisms. These microorganisms are bacteria and fungi, which are present in the soil and elsewhere.
A disadvantage of the known biodegradable nonwovens is the anisotropy that is intrinsic to all staple fiber products, and that is disadvantageous particularly in terms of their mechanical properties, such as strength, which is different lengthwise and crosswise, and it can easily be appreciated that this limits and hinders the utility properties. A further criterion is the fastening of the biodegradable short fibers, which usually most be done with additional binders, since natural fibers are known not to have any thermoplastic properties. Such binders are critical, because of the possible irritation of the skin or problems in wound compatability that may arise; in addition, they are usually not biodegradable.
Spunbonded fabrics of continuous polymer filaments are often preferred, therefore; these have the same strength properties in all directions, are often more-hygienic in use because of the smooth surface of the polymers, and can be easily joined together by heat, in other words welded, because of their thermoplastic properties. Their production is described, for instance, in German Patent 31 51 322, in which the filament polymer is polypropylene.
2. Description of the Related Art
Continuous polymer filaments, as components of spunbonded fabrics that are made of biodegradable polymers, such as thermoplastic cellulose derivatives, are not known to the present applicant; this is due to the difficulties these degradable polymers present in melt spinning: just above the melting temperature, these polymers remain so viscous that they cannot be spun into filaments; if the temperature is raised further, decomposition usually ensues immediately.